Building a PC - data storage

What's going on inside a computer's hard drive?
13 March 2018

Interview with 

Nick Batterham - Cambridge University

hard drive.jpg

hard drive


Naked Scientist Katie Haylor took up the challenge of building a desktop PC with the help of Nick Batterham from Cambridge University's Department of Computer Science and Technology. Step 3 - add a hard drive...

Nick - There are two types of storage device: there’s the RAM - the random access memory. This is the memory that will go on the motherboard.

Katie - These are green, almost a tiny ruler? It’s green on the base and then some gold etchings along the side, and it looks like you’ve got some electronic components sitting on this RAM.

Nick - Each one of these sticks is actually called a DIM. The actual memory are these little black chips that are mounted on the surface. And they have them on both sides, so this particular Dym is 2 gigabytes and we have two of those so that means we have 4 gigabytes in this system, total. The processor can communicate with this, retrieve the information it needs or write new information to it much faster than your hard disk, but this type of memory is volatile. When you turn the power off you will lose whatever you stored in it. They go in these sockets here.

Katie - It’s a bit like teeth, they just slot in either side of these groves?

Nick - That’s right.

Katie - It sounds like it’s gone in.

Nick - Yep.

Katie - You said that this was volatile memory in that when you switch off your computer that’s gone. What about non-volatile memory? Is this where the hard drive comes in?

Nick - Yes, that’s right. But it’s construction is completely different.

Katie - You’re holding it right now and it’s a box. It’s got some plastic on the side and then metal in the middle and once you’ve just turned it over I can see some circuitry. Is it possible for us to look inside because I think you mentioned this was a little bit like a record player, right? You’ve got things that spin...

Nick - Don’t take it too literally, but yes, kind of…

Hard disc drives are about the size of a pack of cards. Nick opened one up so we could see what was inside.They contain a stack of small, brown magnetic discs referred to as "platters", that are each a bit like a mini LP.

Sitting above each platter is an arm, like the needle you’d see on a record player.
When the hard disc is connected, the platters spin at high speed. The drive keeps an index of where all of the information is stored on the platters, or where it has free space, so it can rapidly move the arm to the correct location to write or read information magnetically to and from the disc surface. Critically, unlike RAM storage, when the computer is shut down, the information remains on the discs, ready for when you next need it or until you overwrite it with something else...

Nick - You can put the hard disc anywhere you like inside the case. The cases normally come with little compartments that are designed to hold the disc.

So these pieces of plastic usually come with the case. You fit them on the edges of your hard disk and that allows you to just slot the disk in somewhere in the case like that.


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